CVE-2026-59220 Open WebUI: ReDoS in skill-mention regexes causes whole-instance DoS on default config
An authenticated user can cause a whole-instance denial of service in Open WebUI by sending a specific chat message that triggers regex backtracking.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-59220?
CVE-2026-59220 is a medium-severity denial of service vulnerability in Openwebui Open Webui, published on 9 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Open WebUI is an extensible, feature-rich, and user-friendly self-hosted AI platform. From 0.9.2 before 0.10.0, the SKILL_MENTION_RE and strip_re regular expressions in backend/open_webui/utils/middleware.py parsed <$skillId|label> skill mentions with overlapping quantifiers, allowing an authenticated chat message containing <$ without a closing > to trigger quadratic backtracking and block the asyncio event loop. This issue is fixed in version 0.10.0.
Weakness: CWE-1333
Which versions are affected by CVE-2026-59220?
3 open source packages ship an affected version, including open-webui. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
open-webui PyPI | From 0.9.2 | 0.10.0 |
open-webui PyPI | From 0.9.2 | 0.10.0 |
open-webui PyPI | From 0.9.2 | 0.10.0 |
Products include Openwebui Open Webui.
How do I fix CVE-2026-59220?
Upgrade open-webui to 0.10.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-59220 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-59220 exists.
Other vulnerabilities in Openwebui Open Webui
- CVE-2026-44551 Open WebUI: LDAP Empty Password Authentication Bypass
- CVE-2026-56400 open-webui - Remote Code Execution via CORS Misconfiguration and Session Validation
- CVE-2024-8017 Cross-site Scripting (XSS) in open-webui/open-webui
- CVE-2026-45672 Open WebUI: Jupyter code execution works despite `ENABLE_CODE_EXECUTION=false` — feature gate bypassed
- CVE-2026-87995 Open WebUI: Same-origin XSS to account takeover via terminal port-preview iframe hardcoding allow-same-origin
Sources
Also known as GHSA-ffpj-xv5c-p3gw, PYSEC-2026-3596.